Synthesis of Doubly Threaded [3]Rotaxanes and Poly[3]rotaxanes Through Component Design

Mechanically interlocked polymers (MIPs) are polymeric materials that are made of individual monomeric components that are constrained in space using a mechanical bond as opposed to standard covalent methods. These materials have received increasing attention due to their wide range of applications and increased synthetic accessibility. Despite this, doubly threaded polyrotaxane materials, which are comprised of doubly threaded ring components connected by dumbbell components, have seen minimal synthetic success. These materials offer potential tunability parameters, synthetic control, and component interactions that are not possible with conventional singly threaded materials. Recently in 2017, a poly(n)catenane derived entirely of interlocking rings was reported for the first time based on a doubly threaded metallosupramolecular polymer (MSP) template. It was then hypothesized that this MSP template could be used to access other classes of mechanically interlocking polymers besides the poly(n)catenane such as the doubly threaded poly[3]rotaxane. This dissertation is the initial synthetic work towards achieving this goal. To do this, the representative monomeric interlocked component, a doubly threaded [3]rotaxane, had to first be well understood. Due to the doubly threaded nature, this study required larger rings than had been traditionally used in a rotaxane structure, and as such the stability of the complex became paramount. Three different sets of [3]rotaxanes that varied in stopper size, stopper arm length, and ring size were synthesized, characterized, and analyzed for their kinetic stability to dethreading. Of the parameters tested, ring size was the most influential on stability, and a fully stable [3]rotaxane could be realized with a 42-atom ring or smaller. The corresponding poly[3]rotaxanes were then synthesized and confirmed to have similar stability behavior. Based on this work, an entire range of doubly threaded interlocked polymers are now possible.